FR2994430A1 - PROCESS FOR PRODUCING DIFLUOROMETHANE - Google Patents

Abstract

The invention relates to a process for the production of difluoromethane comprising the catalytic reaction of dichloromethane with hydrogen fluoride in the liquid phase, in the presence of chlorine, and in the presence of an ionic liquid catalyst consisting of the product of the reaction of pentachloride d antimony with an organic salt of the general formula XA wherein A- is a halide or hexafluoroantimonate anion and X is a quaternary ammonium, quaternary phosphonium or ternary sulfonium cation. The invention also relates to an installation adapted to the implementation of this method.

Description

FIELD OF THE INVENTION The present invention relates to a process for the production of difluoromethane and to an installation adapted to the implementation of this process. BACKGROUND Difluoromethane (F-32) can be made by fluorinating dichloromethane or methylene chloride (F-30). For example, documents FR 2736050 and FR 2748022 describe the fluorination of F-30 in F-32 in the gas phase, in the presence of solid catalysts. US Pat. No. 6,268,540 describes the liquid phase fluorination of hydrohalomethanes, and in particular that of F-30, using pentavalent molybdenum halide, niobium, titanium or tantalum halide catalysts.

The short duration of the reactions illustrated does not allow to understand the life of these catalysts. US 6,407,296 describes the use of antimony pentafluoride, or a mixture of antimony pentafluoride and antimony trifluoride, for the production of F-32 in the liquid phase. This catalyst is however very corrosive, and in fact the use of a special alloy for the reactor is necessary. The document WO 99/25670 describes a fluorination of F-30 in F-32 in the liquid phase, in the presence of catalysts such as antimony pentachloride and in a reactor coated with fluoropolymer, for example (which proves to be essential because the corrosion effects that are generated). The document provides for the separation of the products resulting from the reaction in two or three columns, so as to recycle the reactants or co-products to the reactor, and to take a stream of F-32 product and a flow of hydrogen chloride, other reaction product, in combination with F-32 or separately. This process generates impurities: chlorodifluoromethane (F-22) and trifluoromethane (F-23).

The document WO 01/81353 describes ionic liquids based on titanium, niobium, tantalum, tin or antimony allowing the implementation of catalytic fluorination in the liquid phase. Among the fluorination reactions mentioned is that of F-30 in F-32.

There is still a need to develop a new difluoromethane production process with improved yield and improved selectivity, while avoiding excessive corrosion. SUMMARY OF THE INVENTION The invention firstly relates to a process for producing difluoromethane comprising the catalytic reaction of dichloromethane with hydrogen fluoride in the liquid phase, in the presence of chlorine, and in the presence of an ionic liquid catalyst consisting of the product of the reaction of antimony pentachloride with an organic salt of the general formula X + A- wherein A- is a halide or hexafluoroantimonate anion and X + is a quaternary ammonium, quaternary phosphonium or ternary sulfonium cation. According to one embodiment, the X + cation is a tetraalkylammonium, trialkylammonium, alkylpyridinium, dialkylimidazolium or trialkylimidazolium cation, preferably a trimethylsulfonium, N-ethylpyridinium, N-butylpyridinium, 1-ethyl-3-methylimidazolium or 1-ethylimidazolium cation. -butyl-3-methylimidazolium; the catalyst being preferably the product of the reaction of antimony pentachloride with 1-ethyl-3-methyl-imidazolium chloride. According to one embodiment, the process comprises a separation of the products resulting from the reaction, allowing: - the removal of a flow of difluoromethane; recovering a flow of chlorine and recycling it to the catalytic reaction. According to one embodiment, the flow of chlorine comprises a mixture of chlorine and difluoromethane, preferably comprising a chlorine content of less than 7.5 vol%. According to one embodiment, the separation of the products resulting from the reaction also makes it possible to recover a flow of reagents and coproducts and its recycling to the catalytic reaction. According to one embodiment, the separation of the products resulting from the reaction comprises successively a first separation making it possible to take a stream of hydrogen chloride, followed by a second separation making it possible to recover the flow of chlorine, followed by a third separation for taking the flow of difluoromethane and preferably recovering the flow of reagents and co-products, each of these separations being preferably a distillation. According to one embodiment, the process comprises, prior to the first separation, a preliminary separation comprising the recovery of a catalyst stream, as well as the recycling thereof to the catalytic reaction stage. According to one embodiment, the method comprises a preliminary step of loading a catalytic reactor, comprising: the injection of a solvent into the catalytic reactor; the dissolution in the solvent of the organic salt of general formula X + A- in which A- is a halide or hexafluoroantimonate anion and X + is a quaternary ammonium, quaternary phosphonium or ternary sulfonium cation; the injection of antimony pentachloride into the catalytic reactor. According to one embodiment, the antimony pentachloride is injected into the sky of the catalytic reactor; or the charging step comprises mixing the pentachloride with the solvent in the catalytic reactor, preferably by means of a stirrer, a static mixer and / or by stirring with an inert gas. According to one embodiment, the solvent is dichloromethane. According to one embodiment, the antimony pentachloride is injected into the catalytic reactor at a flow rate of 0.1 to 10 tonnes / hour, preferably 0.1 to 1 tonne / hour, and ideally about 0.5 ton / hour.

According to one embodiment, the process optionally further comprises the production of chlorofluoromethane, and the production of difluoromethane and optionally of chlorofluoromethane is from 0.5 to 10 mol / h / L, preferably from 1 to 5 mol / h / L. According to one embodiment, the process comprises the collection of a stream of difluoromethane product with a purity greater than or equal to 98%, preferably greater than or equal to 99%, and more preferably greater than or equal to 99, 9%. The invention also relates to a plant for producing difluoromethane, comprising: a catalytic reactor adapted to carry out the catalytic reaction in the liquid phase of dichloromethane with hydrogen fluoride in the presence of chlorine, the reactor containing an ionic liquid catalyst consisting of reaction product of antimony pentachloride with an organic salt of the general formula X + A- wherein A- is a halide or hexafluoroantimonate anion and X + is a quaternary ammonium, quaternary phosphonium or ternary sulfonium cation; a feed pipe for dichloromethane feeding the catalytic reactor; and a pipe for withdrawing products from the reaction connected at the outlet of the catalytic reactor.

According to one embodiment, the X + cation is a tetraalkylammonium, trialkylammonium, alkylpyridinium, dialkylimidazolium or trialkylimidazolium cation, preferably a trimethylsulfonium, N-ethylpyridinium, N-butylpyridinium, 1-ethyl-3-methylimidazolium or butyl-3-methylimidazolium; the catalyst being preferably the product of the reaction of antimony pentachloride with 1-ethyl-3-methyl-imidazolium chloride. According to one embodiment, the installation comprises: equipment for separating the products resulting from the reaction fed by the withdrawal line of products resulting from the reaction; a difluoromethane sampling line from the equipment for separating the products resulting from the reaction; - A chlorine recycling line from separation equipment of products from the reaction and supplying the catalytic reactor.

According to one embodiment, the installation comprises a recovery line of reagents and coproducts from the equipment for separating the products resulting from the reaction and supplying the catalytic reactor. According to one embodiment, the equipment for separating the products resulting from the reaction comprises a first separation unit at the outlet of which is connected a hydrogen chloride sampling line, a second separation unit fed by the first separation unit. and at the output of which is connected the chlorine recycling line, and a third separation unit fed by the second separation unit and at the output of which is connected the difluoromethane sampling line and preferably at the outlet of which is also connected recovery of reagents and co-products; and, preferably, said first, second and third separation units are distillation columns. According to one embodiment, the installation comprises a preliminary separation unit between the catalytic reactor and the first separation unit, supplied by the withdrawal pipe for products resulting from the reaction, and at the outlet of which is connected a recycling line. catalyst supplying the catalytic reactor. According to one embodiment, the catalytic reactor is made of metal and preferably is provided with a heating jacket; and / or the equipment for separating the products resulting from the reaction are made of metal. According to one embodiment, the plant comprises means for injecting antimony pentachloride and solvent into the catalytic reactor, preferably in the sky thereof. According to one embodiment, the catalytic reactor is provided with means for mixing antimony pentachloride and solvent, which are preferably chosen from a stirrer, a static mixer and means for mixing with an inert gas. The present invention overcomes the disadvantages of the state of the art. In particular, it provides a novel process for the production of difluoromethane having improved yield and improved selectivity. In addition, in this process, the effects of corrosion are controlled, and the scheme of the process is very simple. The product obtained has a high purity. The productivity obtained is also high, as is the life of the catalyst. This is accomplished by carrying out the fluorination of F-30 to F-32 by liquid phase hydrogen fluoride (in the presence of chlorine) by means of an ionic liquid catalyst consisting of the product of the reaction of antimony pentachloride with an organic salt of the general formula X + A- wherein A- is a halide or hexafluoroantimonate anion and X + is a quaternary ammonium, quaternary phosphonium or ternary sulfonium cation. Comparing the use of the above catalyst with another ionic liquid proposed in the state of the art for the fluorination of F-30 to F-32, ie the catalyst obtained by reaction of Emulsion, Cl with chlorotetrafluoro-antimony (SbF4C1), it is found that the yield and selectivity are improved thanks to the invention (compare in particular example 7 below with Example 26 of WO 01/81353).

If one compares the use of the above catalyst with the use of SbC15 alone (which is taught for example in WO 99/25670), it is found that the invention also makes it possible to reduce corrosion (see FIG. Example 10 below).

In addition to the above objects, the invention relates to a method for charging a catalytic reactor adapted to the catalytic reaction of dichloromethane with hydrogen fluoride in the presence of liquid phase chlorine, comprising: injection of a solvent in the catalytic reactor; the dissolution in the solvent of an organic salt of general formula X + A- in which A- is a halide or hexafluoroantimonate anion and X + is a quaternary ammonium, quaternary phosphonium or ternary sulfonium cation; the injection of antimony pentachloride into the sky of the catalytic reactor; or injecting antimony pentachloride into the catalytic reactor and mixing it with the solvent in the catalytic reactor, preferably by means of a stirrer, a static mixer and / or by stirring with a gas inert. According to one embodiment of this catalytic reactor charging process, the X + cation is a tetraalkylammonium, trialkylammonium, alkylpyridinium, dialkylimidazolium or trialkylimidazolium cation, preferably a trimethylsulfonium, N-ethylpyridinium or N-butylpyridinium cation, ethyl-3-methyl-imidazolium or 1-butyl-3-methylimidazolium; the organic salt is preferably 1-ethyl-3-methylimidazolium chloride.

According to one embodiment, the solvent is dichloromethane. According to one embodiment, the antimony pentachloride is injected at a flow rate of 0.1 to 10 tonnes / hour, preferably 0.1 to 1 tonne / hour, and ideally about 0.5 tonnes / hour.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 schematically represents an embodiment of an installation according to the invention. DESCRIPTION OF EMBODIMENTS OF THE INVENTION The invention is now described in more detail and in a nonlimiting manner in the description which follows.

Unless otherwise stated, all percentages given below are percentages by mass. The invention provides for the fluorination of F-30 to F-32 with liquid phase hydrogen fluoride in the presence of chlorine and a catalyst. As regards the description of the catalyst, reference may first be made to WO 01/81353. This catalyst is a non-aqueous, aprotic and liquid ionic compound in a range of moderate temperatures (preferably below 120 ° C) at atmospheric pressure. It is obtained by reacting a halogenated Lewis acid, which is antimony pentachloride (SbCl5), with a salt of the general formula X + A-, in which A denotes a halide anion (bromide, iodide and, preferably chloride or fluoride) or hexafluoroantimoniate (SbF6-) and X + a quaternary ammonium, quaternary phosphonium or ternary sulfonium cation. In the X + A- salt, the X + cation may satisfy one of the following general formulas: R1R2R3R4N + R2R3R4p + R1R2R3s + in which the symbols R1 to R4, which are identical or different, each denote a hydrocarbyl, chlorohydrocarbyl, fluorohydrocarbyl, chlorofluorohydrocarbyl or fluorocarbyl group having 1 to 10 carbon atoms, saturated or unsaturated, cyclic or not, or aromatic, one or more of these groups may also contain one or more heteroatoms such as N, P, S or O.

The ammonium, phosphonium or sulphonium X + cation may also be part of a saturated or unsaturated heterocyclic ring, or aromatic ring having from 1 to 3 nitrogen, phosphorus or sulfur atoms, and respond to one or the other of the formulas following general terms: R2 where R1 and R2 are as previously defined. It is also possible to use a salt containing 2 or 3 ammonium, phosphonium or sulphonium sites in the formula. As examples of salts X + A-, mention may be made of tetraalkylammonium chlorides and fluorides, tetraalkylphosphonium chlorides and fluorides, and trialkylsulfonium chlorides and fluorides, alkylpyridinium chlorides and fluorides, dialkylimidazolium chlorides, fluorides and bromides. and chlorides and fluorides of trialkylimidazolium. More particularly preferred are fluoride or trimethylsulfonium chloride, N-ethyl-pyridinium chloride or fluoride, N-butyl-pyridinium chloride or fluoride, 1-ethyl-3-methyl-1-ethyl-1-ethyl chloride or fluoride. imidazolium, and 1-butyl-3-methylimidazolium chloride or fluoride. The preferred salt is 1-ethyl-3-methylimidazolium chloride, denoted Emim-Cl. The ionic liquids according to the invention can be prepared by suitably mixing the halogenated or oxyhalogenated Lewis acid and the organic salt X + A- in a molar ratio which may range from 0.5: 1 to 3.5: 1 preferably from 1: 1 to 2.5: 1 and more preferably 1: 1 to 2: 1. A molar ratio strictly greater than 1: 1 is particularly recommended if it is desired to obtain an acidic ionic liquid. The mixture can be produced in an autoclave type reactor, optionally cooled to limit the exotherm of the reaction. This exotherm can also be controlled by gradually adding one of the reagents to the other. When the molar ratio of Lewis acid / organic salt is greater than 1: 1, it may be useful to heat the reaction mixture until complete dissolution of the solid.

The reagents and the ionic liquid obtained being generally hygroscopic, the synthesis is advantageously carried out in the absence of air and water. A solvent is used for the preparation of the ionic liquid above. It is advantageously F-30. Advantageously, the mixture is produced in the catalytic reactor used for carrying out the conversion of F-30 to F-32.

It has moreover been found that the method of mixing the reagents has an importance for the performance of the ionic liquid obtained. Advantageously, the mixture is carried out by (1) dissolving the organic salt in a solvent, preferably F-30, and (2) adding the antimony pentachloride gradually in the reactor skies, that is, say above the solution.

The density of SbCl5 is 2.36 g / cm3 and is greater than the density of the Lewis acid solution (a typical density of a solution of Emim-CI / F-30 used in connection with The invention is about 1.3 g / cm3 - for a weight ratio of 1: 1). By introducing the SbCl5 into the reactor skies, that is to say above the solution, the SbCl5 falls to the bottom of the reactor, ensuring maximum contact with the Emim-Cl solution. Injection by the bottom of the reactor with a dip tube does not guarantee such maximum contact, and the SbCl5 tends to remain towards the bottom of the reactor. This leads to parasitic chlorination reactions of Emim, and thus to a reduction of a portion of the antimony to the oxidation state +3 (SbCl3 form), which is detrimental to the catalyst. Therefore, the introduction of SbCl5 into the reactor skies favors the appearance of the desired product. It should be emphasized that the fluorination reactors generally do not comprise mixing means; in this case, the introduction mode of SbCI5 can be critical. Alternatively, it is also possible to use specific means to ensure the homogeneity of the medium: stirring of the medium with an inert gas, use of an agitator, use of a static mixer ... In these situations, it It is possible to introduce SbCl 5 at any level of the reactor, for example at the bottom of the reactor. With reference to FIG. 1, the plant according to the invention comprises a catalytic reactor 5 for carrying out the fluorination reaction of F-30 at F-32. The manufacture of the catalyst ionic liquid described above can be carried out in this reactor, or optionally be carried out separately, in another reactor. The catalytic reactor 5 is preferably supplied with a dichloromethane feed line 2, a chlorine feed line 1 and a feed pipe for hydrogen fluoride 1. Heating means 4 are preferably provided for preheating the reagents prior to their arrival in the catalytic reactor 5. The aforementioned feed lines can feed the catalytic reactor 5 separately or can be connected together upstream of the catalytic reactor 5 to feed it as a mixture of reagents. According to one embodiment, the flow of chlorine is mixed with the flow of F-30, and this mixture is in turn mixed with the flow of hydrogen fluoride. The catalytic reactor 5 is preferably a metal reactor. Indeed, the corrosion problems encountered in the state of the art and in particular in the document WO 99/25670, because of the excess of hydrogen fluoride generally used, are not present in the present case, because the use of an ionic liquid as described above as a catalyst.

The reactor metal may preferably be stainless steel 3161. However, other materials such as a super-austenitic stainless steel or a passivable nickel base alloy may also be employed. For the same reasons, all the other equipment of the installation and in particular all of the separation columns or distillation columns may be metal. The catalytic reactor 5 may comprise a heating jacket or an internal coil allowing, in combination with the heating means 4 upstream, to bring the reaction mixture to the desired temperature. For example, in the catalytic reactor 5, the temperature may be from 50 to 150 ° C, and more particularly from 90 to 110 ° C, and in particular from 100 ° C approximately; and the pressure can be 5 to 40 bar absolute, preferably 13 to 17 bar absolute, and in particular about 15 bar absolute. A product withdrawal pipe from the reaction 6 is connected at the outlet of the catalytic reactor 5. This pipe carries a flow containing the desired product (F-32) mixed with the ionic catalyst, the unreacted reagents (F-30 and hydrogen fluoride), chlorine, and co-products and by-products of the reaction. The withdrawal line of products from reaction 6 feeds a preliminary separation unit 7, which is preferably a distillation column provided with an overhead reflux system. This preliminary separation unit 7 ensures the separation of the ionic liquid (with most of the HF and F-31, or chlorofluoromethane, which is a co-product of the reaction) from the rest of the products resulting from the reaction. The ionic liquid is returned to the catalytic reactor 5 via a catalyst recycling line 8 connected at the bottom of the preliminary separation unit 7. At the head of the preliminary separation unit 7 is connected a first intermediate pipe 9, which is intended for the collection of the remaining reaction products, and feeds a first separation unit 10 for the separation of hydrogen chloride, which is a co-product of the reaction.

Cooling means may be provided on the first intermediate pipe 9 so that the first separation unit 10 operates at the desired temperature. The first separation unit 10 is preferably a distillation column provided with a bottom reboiler and an overhead reflux system. It may for example be operated at a pressure slightly lower than that of the catalytic reactor 5, and especially at a pressure of 5 to 40 bar absolute, preferably 12 to 16 bar absolute, and in particular about 14 bar absolute. The temperature at the bottom of the first separation unit 10 is, for example, 5 to 40 ° C, preferably 15 to 30 ° C, and especially about 22 ° C. The temperature at the top of the first separation unit 10 is for example -35 to 0.degree. C., preferably -25 to -10.degree. C., and especially about -21.degree. At the top of the first separation unit 10 is connected a hydrogen chloride sampling line 11, from which is taken a stream comprising mainly hydrogen chloride (generally with a high purity). Traces of F-32 may also be present in this stream. The HCI produced is preferably recovered in the form of HCl solution after adiabatic or isothermal absorption in water. HCI can be purified by passing the gas through alumina towers to obtain a quality of analysis. For the purpose of energy optimization, heat exchange means can be provided between the hydrogen chloride sampling line 11 and the first intermediate pipe 9, the flow of hydrogen chloride thus absorbing calories from the flow intended at the first separation unit 10. At the bottom of the first separation unit 10 is connected a second intermediate transport pipe 12, which is intended for the collection of the remaining reaction products, and feeds a second separation unit 13 for at the separation of chlorine. Cooling means and pumping means may be provided on the second intermediate transport pipe 12, so that the second separation unit 13 operates at the desired temperature and at the desired pressure. The second separation unit 13 is preferably a distillation column provided with a bottom reboiler and an overhead reflux system. It may for example be operated at a pressure of 10 to 45 bar absolute, preferably 25 to 35 bar absolute, and in particular about 28 bar absolute. The temperature at the bottom of the second separation unit 13 is, for example, 30 to 70 ° C, preferably 40 to 60 ° C, and in particular approximately 50 ° C. The temperature at the top of the second separation unit 13 is, for example, 25 to 65 ° C, preferably 35 to 55 ° C, and in particular approximately 44 ° C. At the head of the second separation unit 13 is connected a chlorine recycling line 14, from which is taken a flow comprising predominantly a mixture of F-32 and chlorine. This chlorine recycling line 14 feeds the catalytic reactor 5, ensuring the recycling in the circuit of chlorine and F-32. Chlorine / F-32 is flammable in a wide range of chlorine concentrations. It is therefore particularly advantageous to adjust the parameters of the installation so that the chlorine / F-32 mixture taken from the chlorine recycling line 14 is not flammable. For example, it may be appropriate to maintain the chlorine content in this mixture at a volume concentration of less than 7.5%. In this way, the mixture is not flammable at a typical temperature of 50 ° C and a typical pressure of 18 bar absolute. At the bottom of the second separation unit 13 is connected a third intermediate transport line 15, which is intended for the collection of the remaining reaction products, and feeds a third separation unit 16 intended for the recovery of the F-32. The third separation unit 16 is preferably a distillation column provided with a bottom reboiler and an overhead reflux system. It may for example be operated at a pressure slightly lower than that of the second separation unit 13, and for example at a pressure of 10 to 40 bar absolute, preferably 20 to 30 bar absolute, and in particular 26 bar absolute about . The temperature at the bottom of the third separation unit 16 is, for example, from 80 to 120 ° C, preferably from 90 to 110 ° C, and in particular from approximately 100 ° C. The temperature at the top of the third separation unit 16 is, for example, from 20 to 60 ° C, preferably from 30 to 50 ° C, and in particular from approximately 43 ° C. At the head of the third separation unit 16 is connected a difluoromethane sampling line 17 through which the F-32 product is collected. This flow of F-32 can be directed to storage units or possibly undergo one or more additional purification steps, for example on activated charcoal or on alumina. At the bottom of the third separation unit 16 is connected a reagent and co-product recovery line 18 which collects the remaining products of the reaction, namely in particular hydrogen fluoride and F-31. The reagent and co-product recovery line 18 supplies the catalytic reactor 5 so as to ensure the recycling of all these compounds in the process. It is possible to install a dryer to remove all traces of water before recycling to the reaction.

The process according to the invention may be discontinuous, semi-continuous or continuous. Preferably it is continuous. Other hydrofluorocarbons are likely to be produced during the catalytic reaction, including F-22 and F-23. If this is the case, almost all of the product F-23 is taken with hydrogen chloride in the hydrogen chloride sampling line 11; and almost all of the product F-22 is withdrawn with the remaining reaction products at the end of all the separation operations, and is therefore recycled to the catalytic reactor 5, where this F-22 is ultimately converted to F-23. The flow of F-32 recovered at the outlet of the installation by the difluoromethane sampling line 17 preferably has a purity greater than or equal to 98%, or 99%, or even 99.9%. This stream preferably contains a water content of less than 15 ppm, an F-31 content of less than 10 ppm, an HCl content of less than 1 ppm and a chlorine content of less than 3 ppm.

The flow of chlorine and F-32 taken from the chlorine recycling line 14 preferably represents a mass flow rate of less than 50% (and, for example, less than 30%, or 20%, or about 10%) of the flow rate. The amount of chlorine present in the plant preferably represents from 0.1 to 2% of the total amount of products circulating in the plant, and in particular from 0 to 10% by weight of the F-32 sample taken from the difluoromethane sampling line. , 2 to 1%, and for example about 0.5%. The underproduction of F-23 represents an amount of less than 2%, preferably less than 0.5%, and typically less than 0.1%, and therefore an overall yield greater than 99.9%. The productivity of F-32 and F-31 is for example 0.5 to 10 mol / h / L, preferably 1 to 5 mol / h / L. A possible variant of the installation illustrated in FIG. 1 consists in reversing the roles of the second separation unit 13 and the third separation unit 16. In this case the modifications of the installation are as follows: the reagent and co-product recovery line 18 is connected at the bottom of the second separation unit 13; the third intermediate transport pipe 15 is connected at the head of this second separation unit 13; the chlorine recycling line 14 is connected to the top of the third separation unit 16; and the difluoromethane sampling line 17 is connected at the bottom of this third separation unit 16. According to this variant, as regards the process, the separation of the products resulting from the reaction comprises, successively, a first separation making it possible to take a flow of hydrogen chloride, followed by a second separation to recover the flow of reagents and co-products, followed by a third separation to take the flow of difluoromethane and recover the flow of chlorine, each of these separations being preferably a distillation. EXAMPLES The following examples illustrate the invention without limiting it. Example 1 - preparation of ionic liquid catalyst without solvent 0.2 mol of SbCl5 is added to 0.1 mol of Emim-Cl. The mixture is slightly heated until a homogeneous mixture is obtained. After cooling, the solid product is analyzed by nuclear magnetic resonance (NMR). The sample is dissolved in deuterated acetonitrile and analyzed by 1H, 13C and 121Sb NMR to establish the structure of the cation of interest. The results are shown in Table 1 below. Example 2 - preparation of ionic liquid catalyst with solvent, using a dip tube 75 g of Emim-CI are dissolved in 200 g of F-30. The equipment used is a glass reactor with a liner connected to an external thermostated bath. A thermocouple indicates the temperature during the operation. The reactor is equipped with a condenser connected to a water circulation. A dip tube is used as a funnel to slowly add 300 g of SbCl5 to the bottom of the reactor. The operation lasts 2 hours, but after about 1 hour, there is crystallization in the mixture. After the end of the addition of SbCl5, the mixture is solidified. The solid is tested by NMR analysis. The results are shown in Table 1 below.

Examples 3 to 6 - preparation of ionic liquid catalyst with solvent, without using a dip tube Example 2 is repeated without the dip tube. The injection point of SbCl5 is the reactor skies, above the Emim-CI / F-30 solution. Two parameters are tested: agitation (yes or no) and temperature during mixing (circulation of water at 20 ° C in the liner or maintenance of a temperature allowing the maintenance of the mixture in liquid form, between 50 and 55 ° C). A sample is taken for NMR analysis. The reaction of Emim-CI with SbCl5 produces a cationic moiety and an anionic moiety. The anionic portion is a halogenated antimony compound, SbCl6-, mixed with neutral compounds such as SbCl5 and SbCl3. The cationic part is a nitrogen cycle. NMR analysis reveals the presence of the following compounds: Emim: C 1 H 3 - Emim-1 Cl: and / or H 3 C CH 3 Cl CI - Emim-2 Cl: H 3 ClN H 3 The chlorination reaction between SbCl 5 and Em C1 leads to a chlorinated cation (mono or disubstituted) and to a reduction of SbCl.sub.5 in SbCl.sub.3. However, SbCl3 is an inactive species, which leads to the formation of SbF3 and to solid deposits in the reactor. Also, this chlorination reaction is not desired.

It is therefore desired to obtain an amount of chlorinated cation (Emim) as low as possible. The results are shown in Table 1 below. Results NMR (% mol) Temperature Agitation Emim Emim-1CI Emim-2C1 Ex. 1 20 ° C No 67.1 29.7 3.2 Ex. 2 20 ° C No 66.4 28.2 5.4 Ex. 3 20 ° C No 87.9 10.5 1.6 Ex. 4 20 ° C Yes 89.6 8.8 1.5 Ex.5 54 ° C No 92.7 7 0.3 Ex.6 54 ° C Yes 86.5 12.9 0.6 Table 1 - Analysis of the Catalyst of Examples 1 to 6 Example 7 - Fluorination reaction The ionic liquid of Example 4 is used for a fluorination reaction of F-30. The equipment used consists of an autoclave with a capacity of 1 liter with a double jacket, made of 316L stainless steel. It is provided with means for measuring temperature and pressure. Apertures at the top of the autoclave allow the introduction of the reagents and the removal of the products. A condenser is provided at the top, as well as a valve for pressure regulation. The condenser is temperature controlled by means of an independent thermostat bath. Its function is to return the entrained catalyst to the reactor, as well as a portion of the unreacted HF and intermediates. The products of the reaction are continuously extracted during the reaction. The exit gas stream passes into a washing device which collects HF and HCl hydracids and is then cooled in liquid nitrogen. The molar distribution of the products of the exit gas is periodically analyzed by GPC (gas chromatography). At the end of the test, the reaction medium is depressurized and slowly heated in order to evacuate the residual HF. During this period of degassing, the organic compounds possibly entrained are also recovered after passing through the washing device in order to remove HF and HCl from the gas stream. In a last step, the autoclave is opened and emptied. The total amount of the mixture of Example 3 (575 g) was transferred to the autoclave. The temperature is adjusted to about 100 ° C in the liquid phase.

The regulation of the pressure is carried out at 15 bar abs. The reagents are then introduced with the following flow rates: 0.3 g / h of chlorine, 25.5 g / h of F-30 and 12 g / h of HF. The molar ratio of HF on the organic compound is thus 2. After having increased the pressure to the desired value and stabilized the continuous flow, the flow rates are increased up to 51 g / h for the F-30 and 24 g / h for HF. The establishment of a correct mass balance between the inlet and the outlet is regularly checked. The composition of the output stream is followed by GC analysis, and reported in Table 2: Time Outlet Molar Composition F-32 F-31 E-30 F-23 6.5 h 70.5% 24.6% 4, 31% 0.225% 22.6h 90.7% 8.9% 0.32% N / a 25.6 H 91.4% 8.3% 0.24% N / A 30.1 H 89.9% 9.7% 0 , 34% Nd 46.9h 89.8% 9.8% 0.27% Nd 51.2 h 90.6% 9.2% 0.21% Nd 55.7h 90.0% 9.7% 0, 27% N / A 72.7h 89.4% 10.3% 0.28% N / A 79.4 H 89.4% 10.3% 0.24% N / A 96.8 H 88.9% 10.7% 0.23 % Nd 103h 89.0% 10.7% 0.28% Nd 109.1 h 87.6% 12.2% 0.22% Nd 126.4 h 87.2% 12.6% 0.22% Nd 137h 87.0% 12.6% 0.38% Nd Table 2 - molar composition of the exit gas (catalyst manufactured by charging SbCl 5 from the top of the reactor) The conversion of F-30 is greater than 99.5%. F-30 and F-31 are recycled as part of a process on an industrial scale and thus converted essentially totally into F-32, the total yield of F-32 that is expected on an industrial scale is greater than 99.5% Productivity in F-32 and F-31 st 1.4 mol / h / L. Example 8 - Fluorination reaction The procedure of Example 7 is repeated, but using the catalyst of Example 2 (mass of 575 g) instead of that of Example 4. The composition of the output stream is followed by GC analysis, and reported in Table 3: Time Molar composition at the outlet F-32 F-31 F-30 F-22 5.2h 4.2% 39.5% 56.3% Nd 9.2h 53.2 % 42.8% 3.9% 0.15% 29.7 h 90.7% 9.1% 0.2% Nd 36.2h 90.9% 7.8% 1.2% Nd 37.0 h 83.2% 13.5% 3.2% 0 50.5 hrs Off: deactivation of the catalyst Table 3 - molar composition of the exit gas (catalyst made by charging SbCl 5 from the bottom of the reactor) Comparison between Example 7 and Example 1 Example 8 illustrates the interest of the procedure for charging SbCl 5 from the top of the reactor in order to prolong the life of the catalyst Example 9 (Comparative) - Fluorination reaction with SbCl 5 alone In this example, fluorination is carried out F-30 in the presence of SbCl5 alone To this end, 147 g of 588 g SbCl5 are added. of F-30 in the same device as that of Example 7. The temperature is adjusted to about 100 ° C in the liquid phase. The regulation of the pressure is fixed at 15 bar abs. The reactants are introduced with the following flow rates: 0.6 g / h of chlorine, 21 g / h of F-30 and 10 g / h of HF. The molar ratio between HF and the organic compound is 2. After increasing the pressure to the desired value and after stabilization of the continuous flow, the flow rates are increased up to 42 g / h for F- and 20 g / h. h for HF. The establishment of a correct mass balance between the entry and the exit and regularly checked. The composition of the output stream is followed by GC analysis, and reported in Table 4: Time Outlet Molar Composition F-32 F-31 F-30 F-22 and F-23 3.9h 68.4% 22.9 % 8.4% Nd 8.9h 83.3% 11.8% 4.7% Nd 14.0 h 84.8% 10.0% 5.0% Nd 19.3 h 85.2% 9.6 % 5.1% N / A 24.4 H 85.5% 9.4% 5.1% N / A 30.4 H 85.7% 9.4% 4.9% N / A 47.2 H 86.5% 8.3 % 5.1% N / A 52.7h 85.4% 9.2% 5.3% N / A 57.3 H 85.0% 10.0% 4.9% N / A 74.5 H 84.4% 10.2% 5.3% Nd Table 4 - Molar Compression of SbCI5 Comparative OZ Example 10 - Corrosion Tests In the context of Examples 7, 8 and 9 above, to evaluate the corrosion rate of the reaction metal coupons are installed in the autoclave. Four 316L stainless steel coupons are placed from the bottom to the top of the liquid phase. The corrosion rates on 316L steel are calculated from the mass loss of metal coupons in the respective tests. The results are reported in Table 5 below. Corrosion rate (mm / yr) Ex.

Ex.8 Ex.

9 Upper part 0.150 0.098 2.2 Upper middle part 0.190 0.122 3.6 Lower middle part 0.280 0.736 3.2 Lower part 0.190 2.203 4.0 Table 5 - Corrosion test results These results illustrate, for example 8, heterogeneity of the liquid medium related to the introduction of high density SbCl 5 into the lower part of the reactor. It is also found that the use of the catalyst according to the invention makes it possible to greatly reduce the corrosion compared with the use of SbCl5 alone.

Claims (5)

REVENDICATIONS1. Process for the production of difluoromethane comprising the catalytic reaction of dichloromethane with hydrogen fluoride in the liquid phase, in the presence of chlorine, and in the presence of an ionic liquid catalyst consisting of the product of the reaction of antimony pentachloride with a salt organic compound of the general formula X + A- wherein A- is a halide or hexafluoroantimonate anion and X + is a quaternary ammonium, quaternary phosphonium or ternary sulfonium cation. 2. Process according to claim 1, in which the X + cation is a tetraalkylammonium, trialkylammonium, alkylpyridinium, dialkylimidazolium or trialkylimidazolium cation, preferably a trimethylsulfonium, N-ethyl-pyridinium or N-butylpyridinium cation, 1-ethyl 3-methylimidazolium or 1-butyl-3-methylimidazolium; the catalyst being preferably the product of the reaction of antimony pentachloride with 1-ethyl-3-methylimidazolium chloride. 3. Process according to claim 1 or 2, comprising a separation of the products resulting from the reaction, allowing: the sampling of a flow of difluoromethane; recovering a flow of chlorine and recycling it to the catalytic reaction. 4. Process according to one of claims 1 to 3, wherein the flow of chlorine comprises a mixture of chlorine and difluoromethane, preferably comprising a chlorine content of less than 7.5 vol%. 5. Method according to one of claims 1 to 4, wherein the separation of the products from the reaction also allows the recovery of a stream of reagents and co-products and its recycling to the catalytic reaction.6. 7. Process according to one of Claims 1 to 5, in which the separation of the products resulting from the reaction comprises successively a first separation making it possible to take a stream of hydrogen chloride, followed by a second separation making it possible to recover the flow of chlorine, followed by a third separation making it possible to take the flow of difluoromethane and preferably to recover the flow of reagents and coproducts, each of these separations being preferably a distillation. A process according to claim 6 comprising, prior to the first separation, a preliminary separation comprising recovering a catalyst stream, as well as recycling it to the catalytic reaction stage. A method according to one of claims 1 to 7, comprising a preliminary step of charging a catalytic reactor, comprising: injecting a solvent into the catalytic reactor; dissolving in the solvent the organic salt of the general formula X + A- wherein A- is a halide or hexafluoroantimonate anion and X + is a quaternary ammonium, quaternary phosphonium or ternary sulfonium cation; the injection of antimony pentachloride into the catalytic reactor. The process of claim 8 wherein the antimony pentachloride is injected into the air of the catalytic reactor; or comprising mixing the pentachloride with the solvent in the catalytic reactor, preferably by means of a stirrer, a static mixer and / or by stirring with an inert gas. The process of claim 8 or 9, wherein the solvent is dichloromethane. Process according to one of Claims 8 to 10, in which the antimony pentachloride is injected into the catalytic reactor at a flow rate of 0.1 to 10 tonnes / hour, preferably of 0.1 to 1 tonne / hour, and ideally about 0.5 ton / hour. 12. Process according to one of claims 1 to 11, optionally further comprising the production of chlorofluoromethane, wherein the production of difluoromethane and optionally chlorofluoromethane is from 0.5 to 10 mol / h / L, preferably from 1 to 5 mol / h / L. 13. Method according to one of claims 1 to 12, comprising the collection of a flow of difluoromethane product with a purity greater than or equal to 98%, preferably greater than or equal to 99%, and more preferably greater than or equal to 99.9%. 14. Difluoromethane production plant, comprising: a catalytic reactor (5) suitable for carrying out the liquid phase catalytic reaction of dichloromethane with hydrogen fluoride in the presence of chlorine, the reactor containing an ionic liquid catalyst constituted by the product; the reaction of antimony pentachloride with an organic salt of the general formula X + A- wherein A- is a halide or hexafluoroantimonate anion and X + is a quaternary ammonium, quaternary phosphonium or ternary sulfonium cation; a dichloromethane feed pipe (2) supplying the catalytic reactor (5); and a product withdrawal line resulting from the reaction (6) connected at the outlet of the catalytic reactor (5). 15. The plant according to claim 14, wherein the X + cation is a tetraalkylammonium, trialkylammonium, alkylpyridinium, dialkylimidazolium or trialkylimidazolium cation, preferably a trimethylsulfonium, N-ethylpyridinium, N-butylpyridinium, 1-ethyl-35 cation. 3-methylimidazolium or 1-butyl-3-methylimidazolium; the catalyst being preferably the product of the reaction of antimony pentachloride with 1-ethyl-3-methylimidazolium chloride. 16. Installation according to claim 14 or 15, comprising: - equipment for separating products from the reaction (7, 10, 13, 16) supplied by the withdrawal line of products from the reaction (6); - A difluoromethane sampling line (17) from the equipment for separating the products from the reaction (7, 10, 13, 16); - A chlorine recycling line (14) from the equipment for separating the products resulting from the reaction (7, 10, 13, 16) and feeding the catalytic reactor (5). 17. Installation according to one of claims 14 to 16, comprising a recovery line reagents and byproducts (18) from the equipment for separating the products from the reaction (7, 10, 13, 16) and feeding the catalytic reactor (5). 18. Installation according to one of claims 14 to 17, wherein the equipment for separating the products from the reaction (7, 10, 13, 16) comprises a first separation unit (10) at the output of which is connected a hydrogen chloride sampling line (11), a second separation unit (13) fed by the first separation unit (10) and out of which is connected the chlorine recycling line (14), and a third separation unit (16) fed by the second separation unit (13) and at the outlet of which is connected the difluoromethane (17) sampling line and preferably at the outlet of which is also connected the reagent and co-product recovery line (18); and wherein, preferably, said first, second and third separation units (10, 13, 16) are distillation columns. 19. Plant according to claim 18, comprising a preliminary separation unit (7) between the catalytic reactor (5) and the first separation unit (10), fed by the line for collecting products resulting from the reaction (6), and at the outlet of which is connected a catalyst recycling line (8) feeding the catalytic reactor (5). 20. Installation according to one of claims 14 to 19, wherein the catalytic reactor (5) is metal and preferably is provided with a heating jacket; and / or in which the equipment for separating the products resulting from the reaction (7, 10, 13, 16) is made of metal. 21. Installation according to one of claims 14 to 20, comprising means for injecting antimony pentachloride and solvent into the catalytic reactor (5), preferably in the sky thereof. 22. Installation according to one of claims 14 to 21, wherein the catalytic reactor (5) is provided with means for mixing antimony pentachloride and solvent, which are preferably selected from a stirrer, a static mixer and stirring means with an inert gas.